Method for continuously casting steel using a partially coated refactory nozzle

ABSTRACT

A method for continuously casting steel in which a refractory nozzle extending downwardly into the molten metal in the mold is coated with a carbonaceous material, for example coal tar pitch. A refractory nozzle coated with a carbonaceous material is also described.

United States Patent 1 1 [111 3,780,788

Sundy Dec. 25, 1973 [54] METHOD FOR CONTINUOUSLY CASTING 3,429,486 2/1969 Cope et a1. 222/D1G. 19

STEEL USING A PARTIALLY COATED 3,628,706 12/1971 Todd 164/335 X REFACTORY NOZZLE Inventor:

George J. Sundy, Bethlehem, Pa.

Assignee: Bethlehem Steel Corporation,

Bethlehem, Pa.

Filed: Sept. 7, 1971 Appl. No.: 178,506

Related US. Application Data No. 857,566, Sept. 12,

Division of Ser.

abandoned.

US. Cl. 164/82, 164/281 Int. Cl B22d 11/10 Field of Search 164/82, 133, 281,

[56] References Cited UNITED STATES PATENTS 3,342,252 9/1967 Wood et al. 164/73 X FOREIGN PATENTS OR APPLlCATlONS 543,639 7/1957 Canada.. 164/337 1,367,501 6/1964 France 164/281 947,626 l/l964 Great Britain 164/281 Primary Examiner-R. Spencer Annear Attorney-Joseph J. OKeefe [57] ABSTRACT A method for continuously casting steel in which a refractory nozzle extending downwardly into the molten metal in the mold is coated with a carbonaceous material, for example coal tar pitch. A refractory nozzle coated with a carbonaceous material is also described.

9 Claims, 1 Drawing Figure METHOD FOR CONTINUOUSLY CASTING STEEL Y USING A PARTIALLY COATED REFACTORY NOZZLE CROSS-REFERENCES TO RELATED APPLICATIONS This is a divisional of original application Ser. No. 857,566 filed Sept. 12, 1969 entitled A Method For Continuously Casting Steel and Means for Accomplishing Same now abandoned.

BACKGROUND OF THE INVENTION In continuous casting of steel, whether from a tundish to a mold or directly from a ladle to a mold, the steel is poured through a refractory nozzle. The nozzle outlet is usually located beneath the top of the molten metal in the mold so that the molten metal will not be in contact with air. U. S. Pat. No. 2,424,640 issued July 29, 1947 to H. W. Spooner entitled Apparatus for Casting Metals Continuously in FIG. 2 shows a tube 45 for transferring molten metal from a receptacle to a continuously casting mold. The tube 45 has the orifice beneath the surface of the molten metal in the mold.

French Pat. No. 1,464,005 issued Nov. 21, 1966 to the Societe Des Usiers Fins De Lest (SAFE) shows a method for continuously casting molten steel from a ladle 1 into a tundish 7 through a nozzle 3 and an extension 5 which has an orifice or exit end below the surface of the molten steel 9 in the tundish 7, and in turn teeming the molten steel 9 from the tundish 7 into a continuously casting mold 14 through a nozzle 13 which has an orifice 15 below the surface of the molten steel 16 in the mold 14. A covering 17 of slag and graphite is provided to cover the surface of the molten steel in the mold 14. Unfortunately, it is impractical to heat the nozzle prior to pouring. Therefore, depending upon the refractory material used to make the nozzle, the nozzle may break because of poor thermal shock resistance or may act as a heat sink and cause the temperature of the metal in contact with the nozzle near and at the surface of the molten metal in the mold to fall below the solidification temperature thereof. As a result, a skull or crust forms atop the molten metal around the nozzle and adheres thereto. When a sufficient weight of skull is formed it will drop into the molten metal and form a portion of the product being continuously cast. The skull is oxidized metal therefore it will not blend into the solidifying molten metal. As a result a large portion, for example 35 feet, of the product, must be discarded prior to rolling into the finished product. While the use of artificial slags can prevent skull formation after the start of teeming, it will not prevent initial skull formation at the start of teeming.

It is an object of this invention to provide a nozzle around which a skull will not form during continuous casting of metal therethrough.

It is an object of this invention to provide a method for continuously casting molten metal which will prevent the formation of a skull at any time during teeming of the molten metal into the mold.

It is another object of this invention to provide a method for continuously casting molten metal which will improve the product yield.

SUMMARY OF THE INVENTION Broadly, the invention includes teeming molten BRIEF DESCRIPTION OF THE DRAWING The drawing is a schematic cross-sectional elevation of a suitable apparatus for practicing the method for continuously casting steel of the present invention.

PREFERRED EMBODIMENT OF THE INVENTION As shown schematically in the figure which depicts conventional casting apparatus suitable for practice of the invention, molten steel 10, which is covered by a layer of slag 11, is teemed from a ladle 12 into a tundish 13 by means of a refractory nozzle 14. The molten steel 15 in the tundish 13, which is also covered with a layer of slag 16, is teemed into a continuous casting mold 17, which can be of any water-cooled design well known in the art, by means of refractory nozzle 18 having the outlet 19 extending below the surface of the molten metal 20 in the continuous casting mold 17. The lower portion of the refractory nozzle 18 is coated with a carbonaceous material 21. The molten metal 20 in the mold 17 is covered with a layer of slag 22.

Nozzles used to teem molten steel continuously into a water-cooled mold are of necessity molded from refractory materials. The nozzles may be of any refractory material resistant to the high temperatures prevalent in the process. Because of the excellent thermal shock resistance of fused silica the use of this material is preferred. However, because the nozzles are not preheated prior to use, a skull forms around the nozzle on the surface of the molten steel in the mold. l have found that fused silica nozzles, the outer surfaces of which are coated with a carbonaceous material, for example coal tar pitch, asphaltic pitch, petroleum tar or pitch, can be used to teem molten steel without the formation of a skull around the nozzle on the surface of the molten steel in the mold. A coating material having a melting point of between 96 F. and 390 F., as determined by the ASTM D-36 ring and ball method is satisfactory. I prefer to use a coal tar pitch which has a melting point of between and F. The coating should cover the nozzle for a distance sufficient to extend above the level of the molten steel when the nozzle is placed beneath the surface thereof, for example to be from onethird to one-half the total length thereof. The interior of the nozzle need not be coated. The coating may be applied by dipping or spraying. A coating thickness of 0.125 inch to 0.005 inch is satisfactory. The coating may be applied by impregnation in lieu of dipping or spraying.

In a specific example of the invention a bifurcated fused silica nozzle, 30 inches long and 4-174 inches in diameter, having a wall thickness of 1 inch, was dipped into a vat containing melted coal tar pitch having a melting point of 147- 152 F. as determined by ASTM D-36. The nozzle was coated with a layer of pitch 0.125

inch in thickness for a distance of 15 inches. The nozzle was used to cast 100 tons of molten steel into an 8 X 37 inches mold. No skull was formed on the surface of the molten steel around the nozzle in the mold during casting.

In another example of the invention a fused silica nozzle, 30 inches long, 4- /5 inches outside diameter and a wall thickness of l-.l/6 inches was coated with coal tar pitch having a melting point of 147 to 152 F as determined by ASTM D-36. The resultant layer of pitch was about 0.125 inch in thickness and extending for a distance of inches along the surface of the nozzle. The nozzle was used to cast 75 tons of steel of molten steel continuously into an 8 X 8 inch mold. No skull formed during casting.

1 claim:

1. in a method for continuously casting molten steel from a receptacle into a water-cooled mold open at both ends through a refractory nozzle partially submerged in the molten steel in the mold, the improvement comprising teeming the molten steel through a fused silica nozzle which is coated for at least the length thereof which is in contact with the molten metal with at least one carbonaceous material taken from the group consisting of coal tar pitch, petroleum pitch and asphaltic pitch, said carbonaceous material having a meltingpoint within the temperature range of 96 to 390 F. whereby the formation ofa skull in the watercooled mold is prevented.

2. The method of claim 1 in which the fused silica nozzle is coated for at least one-third of the length thereof.

3. The method of claim 1 in which the fused silica nozzle is coated for at least one-half of the length thereof.

4. The method of claim 1 in which the coating is coal tar pitch.

S. The method of claim 1 in which the melting point of the carbonaceous material is within the temperature range of to F.

6. The method of claim 2 in which the coating is coal tar pitch.

7. The method of claim 2 in which the melting point of the carbonaceous material is within the temperature range of 140 to 160 F.

8. The method of claim 1 in which the coating is coal tar pitch having a melting point within the temperature range of 140 to 160 F.

9. The method of claim 2 in which the coating is coal tar pitch having a melting point within the temperature range of 140 to 160 F. 

1. In a method for continuously casting molten steel from a receptacle into a water-cooled mold open at both ends through a refractory nozzle partially submerged in the molten steel in the mold, the improvement comprising teeming the molten steel through a fused silica nozzle which is coated for at least the length thereof which is in contact with the molten metal with at least one carbonaceous material taken from the group consisting of coal tar pitch, petroleum pitch and asphaltic pitch, said carbonaceous material having a melting point within the temperature range of 96* to 390* F. whereby the formation of a skull in the watercooled mold is prevented.
 2. The method of claim 1 in which the fused silica nozzle is coated for at least one-third of the length thereof.
 3. The method of claim 1 in which the fused silica nozzle is coated for at least one-half of the length thereof.
 4. The method of claim 1 in which the coating is coal tar pitch.
 5. The method of claim 1 in which the melting point of the carbonaceous material is within the temperature range of 140* to 160* F.
 6. The method of claim 2 in which the coating is coal tar pitch.
 7. The method of claim 2 in which the melting point of the carbonaceous material is within the temperature range of 140* to 160* F.
 8. The method of claim 1 in which the coating is coal tar pitch having a melting point within the temperature range of 140* to 160* F.
 9. The method of claim 2 in which the coating is coal tar pitch having a melting point within the temperature range of 140* to 160* F. 